PROJECT SUMMARY The purpose of this Mentored Patient-Oriented Research Career Development Award (K23) application is to provide research training for Dr. Megan Streur, a post-doctoral fellow at the University of Washington School of Nursing who is transitioning into a faculty role. The long-term training goals of the candidate are to design R- series studies that test biobehavioral interventions aimed at improving atrial fibrillation (AF) symptom management and patient-centered outcomes, and to independently lead and conduct interdisciplinary research projects. AF is the most common cardiac arrhythmia and most individuals with AF experience symptoms, which often negatively impact quality of life. Improved knowledge of the biological and behavioral basis of AF symptoms will lead to the development of targeted biobehavioral symptom management interventions, with the potential to improve quality of life and other patient-centered health outcomes. This career development award will support the applicant's training and research goals through the provision of mentorship, coursework, and other training activities directly relevant to the content areas of advanced statistical and mixed methods for longitudinal clinical research, AF biomarkers, pathology, and treatment, intervention development and clinical trial design, and career development. The research project proposed in this application will examine the biological and behavioral basis of AF symptoms. The applicant proposes a prospective single group (N=50), longitudinal, mixed-method study of adults with newly diagnosed AF (past 3 months). The qualitative component of the study will use a purposive maximum variation sampling (N=20). Notably, we will use novel smartphone-based electrocardiogram (ECG) technology to quantify the time spent in AF and examine the relationship between heart rhythm and symptoms (fatigue, shortness of breath, palpitations). Specifically, this study aims to: 1) Describe concurrent and longitudinal relationships among AF symptoms (fatigue, shortness of breath, palpitations), psychological responses (anxiety, depression), and biomarkers (heart rhythm, TNF-?, norepinephrine, BNP), 2) Examine the effects of AF symptoms, psychological responses, and biomarkers on health outcomes (QoL, healthcare utilization, and treatment strategy) across time, and 3) Characterize symptom experiences and AF-related concerns in relation to health outcomes across time. Descriptive statistics, cross-lagged panel models, and multilevel modeling will be used to achieve aims 1 and 2. Qualitative description and content analysis will be used to achieve aim 3. Both the short and long-term goals of this Career Development Award align with the strategic mission of The National Institute of Nursing Research to understand the biological and behavioral mechanisms of symptoms.